To bond an electrode of an electronic component such as a semiconductor die and an electrode of a circuit pattern formed on a circuit substrate, there have been used methods in which a solder bump is formed on an electrode pad of an electronic component such as a semiconductor die, the formed solder bump is placed downward to face the electrode of the circuit substrate, and they are bonded by heating (see, for example, Patent Document 1). However, when solder is used in an attempt to bond electronic components in a multilayered manner as in a conventional technique described in Patent Document 1, heat applied during bonding may cause melting of a bonded metal formed earlier, resulting in reduced reliability of bonding. For this reason, various methods using metal nanopaste including metal supermicroparticles have been proposed as methods for bonding electrodes without using a solder bump.
Patent Document 1 proposes a method in which a ball of silver microparticle paste prepared by dispersing silver supermicropowder in a solvent is formed on a terminal electrode of a circuit substrate, an electrode of a semiconductor device is bonded by the face-down technique on the ball formed on the terminal electrode of the circuit substrate, and then, after the solvent such as toluene contained in the silver microparticle paste is vaporized, the semiconductor device and the circuit substrate are electrically bonded by sintering at a temperature of 100 to 250° C.
Patent Document 2 relates to a metal nanoparticle liquid dispersion which is capable of forming a coating layer layered such that it has a cylindrical shape having a circular base in which the height is approximately equal to or greater than the radius of the base, by ejecting the metal nanoparticle liquid dispersion by means of inkjet or other methods, and subsequently preparing a sintered column of metal by low-temperature sintering, and proposes a metal nanoparticle liquid dispersion which, as a result of adjusting components of the solvent, has viscosity properties such that it has a low viscosity when the metal nanoparticle liquid dispersion is ejected in the form of microdroplets, it acquires a viscosity that enables the coating layer to be layered in the form of a column-shaped structure as the solvent evaporates during the time after the microdroplets are ejected until they reach an electrode surface, and, after reaching the electrode surface, it can be squeezed from between the metal nanoparticles during the low-temperature sintering. Patent Document 2 further proposes using this metal nanoparticle liquid dispersion to form a conductive wiring layer on a wiring substrate.